LIFESCI 2A03 Lecture Notes - Lecture 6: Thymidine, Cestoda, Chromosomal Translocation

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LECTURE 6 LIFESCI 2A03
1
Molecular Basis of Regeneration: Planarians as a Model System
October 22, 2013
Introduction: Planaria Regeneration and Stem Cells
http://www.hhmi.org/biointeractive/stemcells/planarian_regen.html
The Problem of Regeneration Alejandra Sanchez Alvarado, Jan 2007
http://www.ibioseminars.org/sanchez/sanchez3.shtml
Planaria free living flat worms; related to parasitic flat worms (eg/ tape worm); live in wet environments; 3-12 mm;
scavengers (Eat remains of other animals)
o Centralized nervous system
o Two lobes (horseshoe shape) connected to ventral cords sending projections to tip of organism; brain controls motion
and musculature of organism
o Muscular pharynx from ventral surface; ingest and excrete food from same opening
o Eye spots detect light, contain pigment cup; organism avoids light
o Most cells act as stem cells; can cut length wise or width wise and will regenerate entire body
o Regeneration is fast and robust; decapitate animal, can regenerate in 7 days to fully functioning organism
Day 1 wound healing
Day 2 unpigmented area; forming epithelium
Day 3 regeneration blastema; white pigmented tissue
Day 4 beginning of photoreceptors (notice anlage); neurons form, pigment cups form, photoreceptors
emerge
Day 5 complete differentiation of missing structures
Day 7 planaria completely competent to respond to light, food, touch
o Schmidtea mediterranea bilaterally symmetric; derivatives of all 3 germ layers form
Complex organ system that sit on top of each other (layers)
Gastrovascular system food processing to serve as a source of carbon; enters through single
opening (part of pharynx) to gut, then dispersed to body; food not digested is excreted from same
pharyngeal opening
Excretory system protophrania; dorsal surface, equivalent to kidneys, two cephalic ganglia sitting
on top of 2 ventral cords that traverse to top of animal; neuronal contact between two ventral cords
that traverse to anterior-posterior axis
Sexual and Asexual Biotypes
Sexual
o Hermaphrodites (testes and ovaries) yet cannot self fertilize
Asexual
o Arose as a result of a chromosomal translocation (from chromosome 1 3); cannot sexually
reproduce
Pinches off at waist to produce two segments that each regenerate to form a full
clone
o Focus most on asexual biotypes for studies
o Small genome, 700 Mb (nucleotides)
o Locomote by cilia that beat in one direction; musculature lifts head and turns body
o Regenerative capacity and plasticity root in neoblasts (undifferentiated cells) that populate the majority of the body
Modern research with planaria
o Simple organism can allow us to extrapolate findings to humans
o Found 240 genes involved in regeneration
o Smed-wi in planaria maintenance of stem cells and regulating function of daughter cells (daughter cells cannot
regenerate
Analogous to piwi in drosophila
Distinguishing stem cells from other cells in the planaria
o Morphology large nucleus, little cytoplasm
o Cell-surface or intracellular protein markers different expression in stem cells and other cells (eg/ in niche)
o Cell proliferation mitotic divisions in stem cells
Techniques
1. Labeling dividing cells
a. BrdU Labeling
b. H3P Antibody
2. Visualization of mRNA in situ hybridization
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Document Summary

Molecular basis of regeneration: planarians as a model system. The problem of regeneration alejandra sanchez alvarado, jan 2007 http://www. ibioseminars. org/sanchez/sanchez3. shtml. Day 2 unpigmented area; forming epithelium. Day 3 regeneration blastema; white pigmented tissue. Day 4 beginning of photoreceptors (notice anlage); neurons form, pigment cups form, photoreceptors emerge. Day 5 complete differentiation of missing structures. Day 7 planaria completely competent to respond to light, food, touch: schmidtea mediterranea bilaterally symmetric; derivatives of all 3 germ layers form. Complex organ system that sit on top of each other (layers) Gastrovascular system food processing to serve as a source of carbon; enters through single opening (part of pharynx) to gut, then dispersed to body; food not digested is excreted from same pharyngeal opening. Excretory system protophrania; dorsal surface, equivalent to kidneys, two cephalic ganglia sitting on top of 2 ventral cords that traverse to top of animal; neuronal contact between two ventral cords that traverse to anterior-posterior axis.

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